In some technical measuring tasks, it is necessary to determine the angular position of a shaft and at the same time, an angular difference in relation to a second (shaft) element. For example, the torque acting on the shaft can be determined from the angular difference between two shaft elements that are connected by means of a torque rod.
One example for its use is a TAS (torque angle sensor), which is attached to the steering shaft of a motor vehicle and is simultaneously intended to output the steering angle and the steering torque (see FIG. 1). To that end, the angles are measured at both ends of a torque element. The torque M is then calculated based on the difference xcex4 between these angles
M=cxc2x7xcex4
(c=the spring rate of the torque element).
The individual angle measurements must as a rule be very precise since the generally quite small difference angles are directly influenced by the imprecisions of the two angle measurements.
For example, a number of optical or magnetic code tracks or multi-pole wheels, which are provided with a digital code, are used for the high precision measurement of the individual angles. In a more robust variation, the tracks are not provided with a digital code, but contain various phase data. These phase data are optically or magnetically detected and converted into corresponding (electrical) phase signals, which are evaluated either through single or multiple use of the classic or modified vernier method (e.g. DE 19506938) or the angle measurement occurs with a method for evaluating N-dimensional phase signals.
The object of the invention is the simultaneous and cost-effective determination of angle xcfx86 and angular difference xcex4 from two ambiguous phase measurements xcex11 and xcex12. The angular difference is calculated not as a difference between two angles, but directly and cost-effectively based on the ambiguous phase measurements. At the same time, an unambiguous angle value is obtained from the phase measurements, which are shifted in relation to one another and are ambiguous.
For example, this permits the rotation angle xcfx86 of a shaft and the torque acting on it to be determined simultaneously. The two ambiguous phase signals xcex11 and xcex12 are obtained through the use of RADAR, lasers, optical, magnetic, or other sensor principles. It is often necessary to obtain these phase signals in turn from a number of phase tracks (e.g. see the tracks 1a, 1b, 2a, and 2b in FIG. 1) with the aid of the vernier principle (classic or modified, possibly cascaded or N-dimensional).
Another possible use is the determination of the angular difference between two phase tracks, which is a result, for example, of manufacturing or installation tolerances (tilt angle). It is necessary to know this angular difference in order to carry out a possible correction of the errors in the signal evaluation caused by these tolerances.
In particular, the invention is suited for use in a TAS (torque angle sensor).
The essence of the invention is a method and a circuit arrangement for direct and simultaneous determination of angle xcfx86 and angular difference xcex4 based on two ambiguous phase measurements xcex11 and xcex12, which are shifted by the unknown angular difference xcex4.
By contrast to the known method, it is not necessary to take the indirect route by means of the two absolute angles and this distinctly reduces the wiring cost.
At the same time, the method noticeably reduces the measurement errors in the individual phase tracks.
The improvement over the known method is particularly noticeable if only the angular difference is to be determined. In this case, the block circuit diagram of the device shown in FIG. 2 is further simplified.